In the past, a vehicle-mounted radar apparatus derives a position or the like of a target with respect to a vehicle (radar apparatus) by transmitting a transmission wave from a transmitter antenna and receiving a reflection wave from the target by a receiver antenna. Specifically, the radar apparatus generates a beat signal by mixing a transmitting signal corresponding to the transmission wave, of which a frequency is changed in a predetermined cycle, and a receiving signal corresponding to the reflection wave. That is, the radar apparatus generates the beat signal based on a frequency difference (beat frequency) between the transmitting signal and the receiving signal in each period including an up period in which the frequency ascends in a predetermined cycle, and a down period in which the frequency descends in a predetermined cycle.
Then, the radar apparatus generates a signal (transformed signal) for every frequency by processing the beat signal through FFT (Fast Fourier Transform), and extracts a signal exceeding a threshold of a predetermined signal level, as a peak signal, among the transformed signals. The radar apparatus derives paired data by pairing the peak signal of the up period and the peak signal of the down period based on a given condition.
The radar apparatus derives paired data (predicted paired data) predicting the current paired data based on the paired data derived in the previous process. The radar apparatus determines whether or not a temporally continuous relationship exists between the predicted paired data and the current paired data. If an actual measured position derived from the current paired data is contained in a predetermined range centered on a predicted position derived from the predicted paired data, the radar apparatus determines that the temporally continuous relationship exists. If each paired data has the temporally continuous relationship, the radar apparatus performs a filtering process on the predicted paired data and the current paired data, and derives the paired data on which the filtering process has been performed as currently determined paired data.
The radar apparatus outputs information, such as position information and relative speed of the target derived from the currently determined paired data, to a vehicle control device, and the vehicle control device performs a necessary vehicle control according to the information about the vehicle. For example, a technique associated with the present invention is disclosed in Patent Document 1.
Patent Document 1: Japanese Patent Application Publication No. 2003-177177A
However, for example, in a case where a preceding vehicle stopped ahead starts, the conventional filtering process has a problem in that since a predicted position and an actual measured position are separated from each other, the temporally continuous relationship is disappeared.
It will be specifically described with reference to FIGS. 1 and 2. FIGS. 1 and 2 are diagrams illustrating the process of determining the current paired data of the preceding vehicle. In FIGS. 1 and 2, “definite values” indicate the determined paired data, “predicted values” indicate paired data predicting the current paired data, and “actual measured values” indicate the current paired data. FIGS. 1 and 2 show schematically the position derived from each paired data. Further, “t” attached to each value indicates a time representing a timing of the deriving process.
The radar apparatus judges whether or not an actual measured value (t) is contained in a predicted range around a predicted value (t). If it is YES, the radar apparatus judges that each value has the temporally continuous relationship. If there is the temporally continuous relationship, the radar apparatus performs the filtering process on the predicted value (t) and the actual measured value (t) to derive a current definite value (t). That is, the current determined paired data is derived.
However, in a case where the preceding vehicle is stopped, as illustrated in FIG. 1, since the previous definite value (t−1) is the stop state, the predicted value (t) is predicted as the stop state, so that the previous definite value (t−1) and the predicted value (t) become the same position. If the preceding vehicle starts in this state, since the predicted value (t) and the actual measured value (t) are separated, the values have the temporally consecutive relationship, but the definite value (t) is pulled close to the predicted position rather than its original position by the filtering process. In the next target deriving process, since a predicted value (t+1) is derived on the basis of the definite value (t), as illustrated in FIG. 2, the current measured value (t+1) is not contained in the predicted range around the predicted value (t+1), and thus there is no temporally continuous relationship. As a result, despite the paired data indicative of the same target as the preceding target, the radar apparatus cannot judge that it is the same target, so that the preceding vehicle is disappeared.